1. Field of the Invention
The invention relates to a device for the central feeding of tanks such as circular grit traps, grit classifiers or settling tanks of circular construction.
The subject of the invention is also a process for feeding such circular grit traps and grit classifiers and settling tanks of circular construction. Finally, the subject of the invention is also the use of the process and of the device for feeding circular grit traps and grit classifiers and settling tanks of round construction in sewage treatment plants.
2. Description of the Prior Art
For reasons of operational reliability, it is usually necessary, in the case of many waste-water and sludge treatment units of the sewage treatment plant, to separate the grits and other mineral substances, which have been entrained in the waste water, from the putrescible, organic substances. The conventional devices for degritting the waste water are, depending on construction type and operation, designated as deep, shallow, circular and aerated grit traps. In the case of the prior-art circular grit traps and grit classifiers of circular construction, the waste water is fed tangentially to a circular hopper-bottomed tank. After flowing through a centering angle of over 180.degree., the waste water passes into the outflow. The great disadvantage with conventional circular grit traps and grit classifiers of circular construction, however, is that, owing to the tangential introduction, the tank volume (region through which flow occurs effectively) provided is not utilized to the optimum degree and the hydraulic efficiency thereof is thus only approximately 50%.
The operating principle of conventional circular grit traps is based on the fact that, in curves, the bed load moves inside the curve. The forced circular motion causes, owing to the centrifugal force in the circular grit trap, a rise in the water level from the rotational axis outwards. Under the influence of the superatmospheric pressure in the edge zone, a circular motion, which is directed towards the center at the bottom, is thus superimposed in the throughflow. This results in a helical flow through the tank. Owing to the radial transverse flow, which is particularly strong at the bottom as a result of the reduced tangential velocity of the waste water there, the grit which has sunk to the bottom is conveyed into the hopper-shaped collecting chamber, in the axis of which there is arranged at least one cylindrical pump pit with mammoth pumps.